Micromechanical gyroscopes which are micromachined from a single silicon substrate are now well known in the art. Such devices typically have a gimbaled structure which includes an inner gimbal ring having a set of flexures coupled to a mass. The inner gimbal ring serves as the sense axis. The inner gimbal ring is located within an outer gimbal ring which serves as the drive axis and is coupled to a gyroscope frame by an outer set of flexures.
The structure of the prior art gimbaled gyroscope requires that the thin inner flexures be surrounded by a thicker gimbal ring or plate. The boron diffusion process utilized to define the gimbal ring and the flexures causes the thicker gimbal Plate to shrink more than the flexures, causing the inner flexures to be in compression, and in some cases to buckle. This buckling introduces variations and uncertainty in the resonant frequency of the inner gimbal member which is difficult to predict and control.
Although the buckling problem can perhaps be eliminated by adding strain relief slots near the inner flexures, the frequency of the gyroscope's dive axis must equal the resonant frequency of the sense axis, requiring prior measurement and trimming of the resonant frequency, precision frequency generators, and precise temperature control.
Alternatively, automatic frequency control loops may be added to control the drive and sense axis frequencies. The control loop signals, however, must be accurate and may interfere with the gyroscope's output signal. In addition, differences in resonant frequency between the drive and sense axes can develop due to minor variations in spring constant of the flexures or work-hardening of the flexures over time.